This research aims to examine in considerable detail the differences in migration streams of older persons, classified by age and sex. This research will enable us, for the first time, to see and to understand the origin/destination patterns and differentials of the "young-old", the "middle-aged-old", and the "old-old". Apart from simple descriptive tabulations and analyses (including measures such as indexes of dissimilarity, preference, concentration and attractiveness), the proposed research will devote a considerable amount of attention to testing various forms of the gravity model (where migration streams are a function of distance between origin and destination as well as the population size at each location) and the stimation of ecological models where migration will be hypothesized to be a function of variables (at origin and at destination, as well as by age/sex where available and appropriate) such as health facilities/services, energy demand/supply/cost, service availability, climate, income, taxation levels, cost of living and so on. Care will be taken to avoid problems of simultaneity in that explanatory variables will be selected for the year (1965) at the beginning of the five year migration period. These procedures will use as dependent variables the preference/attractiveness/concentration indexes as well as the relative size of the flows themselves. The procedures will allow us to make some assessment of the different behavioral patterns of various age-sex groups. The results of this analysis will be used to make forecasts of the elderly population, by age and sex, at the state level for 1975. These will be compared with existing estimates and surveys (such as those prepared for the National Cancer Institute and the results of the Survey of Income and Education) to establish the predictive utility of these gravity and ecological models. Greater age/sex detail is possible through these procedures than from existing sources; lacking a mid-decade census, such estimates will be crucial for program planning and service delivery in the 1980s.